1. Field of the Invention
The present invention relates to an anti-tumor immune response, and in more detail, to a method for inducing immune responses specific to tumor associated antigen that acts specifically on tumor cells.
2. Description of the Related Art
In the current cancer treatment, after cancer tissues are removed as much as possible, the remaining cancer cells are killed by radiotherapy and chemotherapy. This is a main method to treat tumors currently. But surgery has several problems like that the removal range is broad and there is recurrent risk by micrometastasis. Radiotherapy and chemotherapy also have many side effects. Especially, in the case of anti-tumor drugs, they are always not effective in all cancer. In many cases, remaining cancer cells that were exposed to anticancer drug have resistance, keep on growing and metastasize to other organs. In the result, the cancer is impossible to be treated.
Accordingly, we have no choice but to admit that there is the limit to conquer cancer by only these therapies. Therefore, immune therapy is now expected as a new cancer treatment, which uses immunity of our body.
The immune therapy has side effects less than other treatments and is more effective in being used in combination with other treatments. So importance of immune therapy is currently revealed. Immune therapy is indirect treatment that treats cancer by activating patient's immune response whereas surgery, chemotherapy and radiotherapy directly attack cancer cells among cancer treatments.
Broadly, the different types of immune response fall into two categories: a humoral immune response and a cell-mediated immune response. The humoral immune systems have a function to make antibodies for degradation and removal of antigens, e.g. infectious microbes, virus and bacteria, invading into the human body. Meanwhile, the cellular immune response relates to immune surveillance mechanism and produces cells (lymphocytes) specific to any antigens.
The cellular immune responses are more important in the tumor-related immunity rather than the humoral immune systems. Like this, antitumor immune response is generally related to cell-mediated responses; therefore it is known that the role of CD8+ cytotoxic T lymphocyte, CTL is important for this reaction. Nowadays, tumor-associated antigen (TAA) has been studied to induce antitumor T cell. Also, the researches for T cell immune therapy against tumor have been continued according to development of recombinant DNA technology.
To induce the antigen-specific cytotoxic T lymphocyte specifically acting to the tumor cell, the presentation of antigen to MHC class 1 molecule is essential. This pathway is initiated as that treatment of large multifunctional proteasome to cellular protein is carried out. And then the antigen was transported into the endoplasmic reticulum through transporter protein associated with antigen processing, bounded with MHC class 1 molecules, and presented to cell surface throughout the golgi apparatus.
But it is characterized that presentation pathway of antigen by MHC class 1 molecule appears only within the cell. So, there has been some tries to directly introduce external protein into MHC class I. Generally, protein introduced for vaccine is known inadaptable to increase antitumor immune response, because it enters into the cell through endocytosis and then stimulates Th(CD4+) cell presented by MHC class II molecules. In the result, it activates humoral immune response instead of cellular immune response.
Therefore, there has been a requirement toward a method for enabling the externally introduced antigen protein to transport into cytoplasm of antigen presentation cell and then the antigen is presented by MHC class I molecules.